chore(deps): bump openpyxl from 3.0.10 to 3.1.5 in /backend

Bumps [openpyxl](https://openpyxl.readthedocs.io) from 3.0.10 to 3.1.5.

---
updated-dependencies:
- dependency-name: openpyxl
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

backend/poetry.lock

@@ -43,7 +43,7 @@ python-redmine = "^2.5.0"
 sentry-sdk = "^2.9.0"
 whitenoise = "^6.7.0"
 django-hurricane = "^1.6.0"
-openpyxl = "3.0.10" # TODO: dependency of `pyexcel-xlsx` Remove as soon as https://github.com/pyexcel/pyexcel-xlsx/issues/52 is resolved.
+openpyxl = "3.1.5" # TODO: dependency of `pyexcel-xlsx` Remove as soon as https://github.com/pyexcel/pyexcel-xlsx/issues/52 is resolved.
 psycopg = {extras = ["binary"], version = "^3.2.1"}
 
 [tool.poetry.group.dev.dependencies]